Colored Pyrotechnic Smoke-Producing Composition

ABSTRACT

A colored pyrotechnic smoke-producing composition has an oxidizer, a fuel, a flame retardant, a dye, a coolant, and a binder. The oxidizer may be potassium chlorate. The fuel may be starch, dextrose, lactose, and/or sucrose. The coolant may be sodium bicarbonate or magnesium carbonate. The binder may be nitrocellulose or a halogen-free thermoplastic. The flame retardant may be one or more nitrogen-rich compounds. The composition may be in pelletized form or in the form of a solid charge. The composition may consist of on a mass basis oxidizer 20-35%, fuel 15-25%, flame retardant 5-15%, dye 27-40%, coolant 8-18%, and binder 1-2%. The invention may be a device consisting of a body filled with the composition and a first fire starter composition, and an attached squib igniter. The body may be a grenade. A process for producing the composition is also disclosed.

FIELD OF THE INVENTION

The present invention relates to a smoke-producing pyrotechniccomposition that is useful primarily in pyrotechnics for the productionof colored smokes. More particularly, the present invention is relatedto generally cool-burning, non-toxic, and non-corrosive smoke producingcompositions, which incorporate at least one affordable nitrogen-richcompound in addition to an oxidizer-fuel system, smoke-formingsubstance, and binder. Affordable nitrogen-rich compounds that aresuitable for use with the current invention can include guanidinenitrate, guanidine carbonate, or dicyandiamide; azodicarbonamide,melamine, and oxamide.

BACKGROUND OF THE INVENTION

Effective and safe generation of colored smoke by the vaporization of anorganic dye poses a challenging pyrotechnic problem. The military andthe fireworks and entertainment industries rely on this technique forthe generation of copious quantities of brilliantly colored smoke.

The requirements for an effective colored-smoke composition include:

-   -   The composition must produce sufficient heat to vaporize the        dye, as well as produce a sufficient volume of gas to disperse        the dye into the surrounding environment.    -   The composition must ignite at a low temperature and continue to        burn smoothly at a low temperature (well below 1000° C.). If the        temperature is too high, the dye molecules will decompose, and        the generated smoke's color quality and volume will deteriorate.        The use of metal fuels should be avoided in colored        smoke-generating compositions because of the high reaction        temperatures they may produce.    -   Although a low ignition temperature is required, the        smoke-generating composition must be stable during manufacturing        and storage over the expected range of ambient temperatures.    -   The molecules creating the colored smoke must be of low toxicity        (including low carcinogenicity). Further, they must readily        sublime without decomposition at the temperature of the        pyrotechnic reaction to yield a dense smoke of good color        quality.

In various contexts, it is desirable to have the capability to producesmoke suitable for a wide variety of applications. For example, theability to produce smoke at a particular location may provide the basisfor a remote signaling system. Such a system may have application insearch and rescue operations and in military exercises. Smoke of aparticular color and density may also be desirable for trainingpurposes. For example, in order to train fire fighters, it would beadvantageous to simulate specific types of smoke produced by variousfire conditions. For individuals working in a fire-prone environment,such as on an aircraft or ship, it would also be desirable to have thecapability of simulating smoke produced by a fire in order to provide arealistic fire drill.

Smoke can be used as a marker for various purposes. A smoke marker canbe seen from substantial distances, both from the ground and from theair. Accordingly, a smoke marker would be useful in military operations,search and rescue, certain types of industrial projects, or in any othersituation in which it is important to find and mark a particularlocation.

In a military context, the need for smoke-producing devices andcompositions is well appreciated. Not only can smoke be used as a markerfor search and rescue, but smoke may also be used to mark a particulartarget. It can also be used as a marker to determine the position ofspecific personnel and equipment.

Smoke can also be used to obscure vision. A smoke shield can be veryhelpful in conducting military operations in order to prevent adverseforces from obtaining a clear view of the operations. For example, itmay be desirable to use a vision obscuring smoke in order to move troopsand equipment under at least partial cover.

Various types of smoke-producing compositions and devices are presentlyknown. It is known how to judiciously select the components of asmoke-producing composition that uses a sublimable organic coloringmedium. By considering the kinetics of combustion and the desired yieldof colored smoke, conventional smoke-producing compositions require astrongly exothermic composition, but struggle to limit the degradationof the coloring medium by combustion. A weakly exothermic composition isunsuitable because it permits only a minimal percentage of coloringmedium and furnishes only a very mediocre smoke yield that is hardlyvisible, especially when there is a cloudy or dark sky. A weaklyexothermic composition also is difficult to ignite to initiate smokeemission.

It is also known that it is advantageous to adjust the combustion speed,because a too rapid combustion provokes the destruction of the coloringmedium or liberates the smoke too briefly or in a non-workable manner.In contrast, a two slow combustion produces a smoke yield of minimalconsequence and tends toward self-extinction of the combustion process.It is known to consider the effects of the reaction thermodynamics bymaking an appropriate choice of the components of the composition and bythe conditions of compression of the composition.

However, most existing smoke-producing compositions have severelimitations. One of the limitations is that of toxicity. Manysmoke-producing compositions incorporate materials that are severelytoxic or become irritants when subjected to the heat necessary toproduce smoke.

A variety of dyes have been used in colored smoke mixtures. Many ofthese dyes are presently under investigation for carcinogenicity andother potential health hazards.

The materials that work best in colored smokes have several propertiesin common:

-   -   Volatility: The dye must undergo a phase change to the gas state        upon heating, without also undergoing substantial decomposition.        Only low molecular weight dyes (less than 400 grams/mole) are        usually used because volatility typically decreases as molecular        weight increases. Salts do not work well: ionic species        generally have low volatility because of their strong        inter-ionic attractions within the crystalline lattice.        Therefore, functional groups such as —COO— (carboxylate ion) and        —NR3+ (a substituted ammonium salt) should be avoided.    -   Chemical stability: Oxygen-rich functional groups (—NO₂; —SO₃H)        should be avoided. At the typical reaction temperatures of smoke        compositions, these groups are likely to release their oxygen,        leading to oxidative decomposition of the dye molecules. Groups        such as —NH₂ and —NHR (amines) are used, but potentially        dangerous oxidative coupling reactions can occur in an oxygen        rich environment.    -   Old-style dyes for military markers and grenades are polycyclic        or aromatic amino, hydroxyl, azo and keto compounds, in which        unsaturation conjugated with the aromatic structure. Such        compounds are known to cause chromosome mutations, which may        lead to cancer. Coloring agents for new munitions are chosen to        minimize potential carcinogenicity, which increases their cost,        but allows recycling of the dyes without high health risks.

Prior art colored smoke formulations have employed the use of mixturescontaining a fuel, an oxidizer, and a dye. The principle behind the useof such formulations lies in the reaction between the fuel and oxidizer,and the accompanying release of a large amount of energy during thereaction. The exothermic reaction releases the energy contained in thebonds of the highly structured fuel molecule as heat. This causes thedye component of the formulation to undergo a series of phasetransitions from a solid to a liquid and ultimately to a gas. However,if the temperature of the fuel-oxidizer reaction is too high, the dyewill degrade, and the quantity and color quality of smoke generated willbe unsatisfactory.

Conventionally, the dye exists as a solid crystal at standardtemperature and pressure. When heat generated by a fuel-oxidizerreaction is applied to the solid crystal, dislocations of the moleculesoccur within the crystalline lattice. As molecules of the dye becomedetached from the central lattice, a liquid is formed. As more heatenergy is applied, the individual molecules of the dye begin to movefaster and faster. The molecules, as a result, translate through space,rotating about the axes of the dye structure, and vibrate in manycomplex modes. This molecular activity is responsible for the transitionof the dye molecules from the liquid phase to the gas phase.

Although heat is required for the dye to undergo the essential phasechanges to produce colored smoke, individual molecules of the dye aresubject to degradation at elevated temperatures. If the molecularstructure of the dye is subject to forces and energies that are greatenough to cleave the molecule's bonds, changes in smoke color or loss ofcolor properties are likely to occur.

Another problem encountered in the search for a desirablesmoke-generating composition is the production of a solid residue asconventional smoke-producing compositions burn. The solid residuereaction product contributes to the formation of waste products such asslag and solid clinkers. When such solid materials accumulate in thecore of a pyrotechnic smoke-producing munition, they prevent the gasphase dye molecules from escaping into the environment. As a result,deflagration can occur, which can cause injury to bystanders, or resultin only a limited release of colored smoke. Furthermore, the formationof slag increases the decomposition of the dye vapor, which may lead tocolor deterioration. Only a few dye materials have been found suitablefor use in prior art smoke-producing compositions that rely upon thevaporization of an organic dye because most dye materials generateexcessive slag or clinkers. The importance of obtaining uniform andporous slag reaction products is already known, as well as thepossibilities of selecting components of the smoke-producing compositionthat enable obtaining such slag. It is also known that the extent ofporosity of the slag regulates the smoke yield and favors heat exchangebetween the components of the smoke-generating composition.

Other known compositions have the drawback of burning at temperaturesthat are too high (600-800° C.) or leave too many carbonaceous residues,which are impermeable to the dye molecules in the gas phase. Theseconditions cause the destruction of the smoke-producing components andtherefore demonstrate poor effectiveness in producing colored smokes.Another drawback may be the rapid ascent of the smoke because of thesmoke's high temperature, which causes the smoke to dissipate tooquickly for the desired effect to be achieved.

Another major drawback of using such mixtures is the hazard created bythe creation of a flame front at the moment of ignition of the mainfilling composition. For example, a smoke grenade has been observed toemit a flame front with a height of approximately 4-10 inches throughthe grenade's emission ports. The flame from was observed to last from1-5 seconds while the smoke charge began burning. This behavior cancreate safety hazards to personnel and equipment, as well as potentiallycausing brush and grass fires in dry environments with significantlyelevated fire danger conditions.

In summary, there is a need for effective colored smoke-producingcompositions. This need exists in both military and civilian operations.However, many smoke-producing compositions presently used are difficultto handle. Many such compositions are toxic and irritating, requiringspecial precautions during use. Many such compositions are alsocorrosive and damaging to both electronic and mechanical equipment.Finally, some compositions produce an excess of heat and flame, againlimiting their usefulness and requiring that additional safety measuresbe taken. For these reasons, conventional smoke-producing compositionsare found to be inadequate

Therefore, a need exists for a new and improved colored pyrotechnicsmoke-producing composition that provides is generally non-toxic andnon-corrosive, does not incorporate toxic or irritating materials suchas zinc, phosphorous, and aromatic organic compounds, which is simple tomanufacture and use, and is still in effective smoke producer. In thisregard, the various embodiments of the present invention substantiallyfulfill at least some of these needs. In this respect, the flamelessigniting slurry composition according to the present inventionsubstantially departs from the conventional concepts and designs of theprior art, and in doing so provides a composition primarily developedfor the purpose of providing a cool-burning, non-toxic, andnon-corrosive smoke producing composition.

SUMMARY OF THE INVENTION

The present invention provides an improved colored pyrotechnicsmoke-producing composition, and overcomes the above-mentioneddisadvantages and drawbacks of the prior art. As such, the generalpurpose of the present invention, which will be described subsequentlyin greater detail, is to provide an improved colored pyrotechnicsmoke-producing composition that has all the advantages of the prior artmentioned above.

To attain this, the preferred embodiment of the present inventionessentially comprises a composition of an oxidizer, a fuel, a flameretardant, a dye, a coolant, and a binder. The oxidizer may be potassiumchlorate. The fuel may be starch, dextrose, lactose, and/or sucrose. Thecoolant may be sodium bicarbonate or magnesium carbonate. The binder maybe nitrocellulose or a halogen-free thermoplastic. The flame retardantmay be one or more nitrogen-rich compounds. The composition may be inpelletized form or in the form of a solid charge. The composition mayconsist of on a mass basis oxidizer 20-35%, fuel 15-25%, flame retardant5-15%, dye 27-40%, coolant 8-18%, and binder 1-2%. The invention may bea device consisting of a body filled with the composition and a firstfire starter composition, and an attached squib igniter. The body may bea grenade. A process for producing the composition is also disclosed.There are, of course, additional features of the invention that will bedescribed hereinafter and which will form the subject matter of theclaims attached.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood and in order that the presentcontribution to the art may be better appreciated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of the manufacturing process for the currentembodiment of the colored pyrotechnic smoke-producing compositionconstructed in accordance with the principles of the present invention.

The same reference numerals refer to the same parts throughout theFIGURE.

DESCRIPTION OF THE CURRENT EMBODIMENT

An embodiment of the process for manufacturing a colored pyrotechnicsmoke-producing composition of the present invention is shown andgenerally designated by the reference numeral 10.

The invention relates to a smoke-producing pyrotechnic composition andmore particularly, is related to generally cool-burning, non-toxic andnon-corrosive smoke producing compositions, which incorporate:

-   -   Oxidizer—a presently preferred oxidizer is Potassium Chlorate        (KCLO₃).    -   Fuel—a low energy fuel is preferred in order to minimize heat        and flame produced. Such fuels may include, for example, starch,        dextrose, lactose or sucrose.    -   Dye—a sublimable and/or evaporable organic coloring substance        which produces a colored smoke as a result of the dye undergoing        a phase change.    -   Coolant—sodium bicarbonate or magnesium carbonate may be added        to act as a buffer for the KCLO₃ and as a further coolant;        presently the preferred coolant is magnesium carbonate.    -   Binder—may be any one of a number of binders such as        nitrocellulose or a polymer binder.    -   Additives—at least one affordable nitrogen-rich compound        selected from the group consisting of guanidine nitrate,        guanidine carbonate or dicyandiamide, azodicarbonamide,        melamine, and oxamide.

It is clear from a vast array of studies that traditional pyrotechnicsare a severe source of pollution. Environmentally friendly or “green”formulations are therefore based on nitrogen-rich compounds to avoid theuse of heavy metals and perchlorates. High-nitrogen compounds gain theirenergetic character not by oxidation of carbon, but from their highheats of formation. They offer not only environmentally compatiblecombustion products, but in many cases even better color quality andintensity than older formulations.

Nitrogen-rich materials combine several advantages:

-   -   only or mostly gaseous products (smokeless combustion)    -   high heats of formation    -   high propulsive powder    -   high specific impulse    -   high flame temperatures

Compounds for use in pyrotechnics should be cheap, easy to produce, andnon-hygroscopic. High nitrogen content is desirable for reduction ofsmoke and particulate matter resulting from combustion. The reactionrate must therefore be adjusted for that purpose. High-energy reactionsare generally classified as “burning” (approximate reaction velocity inthe range of mm or cm s⁻¹), “deflagration” (m s⁻¹), or “detonation” (kms⁻¹).

An ideal dye material for this application transforms “sublimes”directly from the solid phase to the gas phase with little or nointermediate liquid phase. The direct transformation to a gas enhancesthe likelihood of the dye molecules escaping from the solid matrix madeof fuel, oxidizer, and dye to the external environment without the dyemolecules reaching an undesirably high temperature. Thus, dyes aresought for the composition that have the property of sublimation atincreased temperatures and normal pressures.

In general, flame suppressant/flame retardant compounds act in one oftwo ways: either by preventing ignition of a product or by preventingthe spread of a fire once a product is ignited. First, the ignitionsusceptibility of a product is lowered when the flame retardantincreases the net heat capacity of the product. Second, once a fire hasalready begun, flame retardants can reduce the tendency of the fire tospread by reacting with the product and forming a less flammable char ornoncombustible gaseous layer along the boundary of the fire. Withinthese two general flame-retardant mechanisms, Kirk-Othmer's Encyclopediaof Chemical Technology (Kirk-Othmer, 2001) provides a more detailedsummary of five specific mechanisms by which flame retardancy may occur:physical dilution, chemical interaction, inert gas dilution, thermalquenching, and protective coatings.

The use of nitrogen-rich compounds as both nitrogen producing agents andflame retardants overcomes many of the severe problems encountered inthe existing art. In particular, the present invention providescompositions that are generally non-toxic, non-corrosive, and that canbe formulated to burn at lower temperatures and with a lower energyoutput while still producing effective smoke output.

If potassium chlorate is used without the addition of a nitrogen-richmaterial to the smoke-producing composition, the combustion temperatureis at least 400° C. (750° F.). At this temperature, the dye is nearlycompletely destroyed, making the composition ineffective at producingsmoke. However, because the present invention adds a nitrogen-richmaterial to the smoke-producing composition, the combustion temperatureof the smoke-generating composition of the present invention is reducedto a range from 100° to 250° C. (200 to 480° F.). At the lower end ofthis range, thermal degradation of the dye is largely prevented,resulting in the effective production of colored smoke. As an example,by using guanidine nitrate in combination with the potassium chlorate,the combustion temperature drops to a range between 190° and 300° C.(375 to 575° F.). The temperature reduction is achieved by the guanidinenitrate catalyzing the decomposition of the chlorate, which makes itpossible for the decomposition reaction to occur at a lower temperaturethan would be conventionally required.

The nitrogen-rich compounds suitable for use in this invention have beenfound to be excellent additives for use in a smoke-producing compositioncontaining a degradable dye. The cited additives have been found to be avery efficient coolant because they are nitrogen producing agents thatact as flame retardants. Because the additives' decomposition processgenerates the liberation of gases (carbon dioxide and nitrogen), theyassist sublimation of the organic dye and provide thermal protectionfrom the fuel-oxidizer reaction. The additives also inhibit slagbuild-up and facilitate the production of uniformly porous slag. Theseslag characteristics enhance the production of color in the smokegenerated. In contrast, conventional pyrotechnic compositions pass thevaporized dye through significant amounts of hot slag of limitedporosity before the dye escapes into the environment, which has adeleterious effect on the color of the vaporized dye.

Nitrogen-rich compounds are not only remarkable energy-rich andoxygen-nitrogen-containing compounds that act exothermically to supplyheat to the smoke-generating reaction. The nitrogen-rich compounds alsosimultaneously yield decomposition products that neutralize the acidsgenerated by the smoke-producing composition of the present invention.

The dyes, which may be used in this invention corresponding to the colorstandard FED-STD-595C color chip, are listed by the Society of Dyers andColorists in dye classification materials according to chemicalstructure, and include the following:

TABLE 1 Chemical compositions of some of the dyes suitable for use in incolored smoke-producing compounds of the present invention CI Name CAS#Trade Name Chemical Name Solvent Red 1 1229-55-6 Anasol Red SGamethoxybenzenazo-β-naphthol Disperse Red 9 82-38-2 Anasperse Red SG1-methylaminoanthraquinone Solvent Orange 7 3118-97-6 Anasol Orange SG1-((2,4-Dimethylphenyl) azo)-2-naphthalenol Solvent Orange 86 81-64-1Anasol Orange HF SG 1,4-dihydroxyanthraquinone Disperse Blue 3 2475-46-9Anasperse Blue SG 1-methylamino-4-ethanolaminoanthraquinone SolventViolet 47 81-63-0 Anasol Violet SG 1,4-diamino-2,3-dihydroanthraquinoneSolvent Yellow 33 8003-22-3 Anasol Yellow SG Mixture of2-(2-quinolinyl)-1,3-indandione and2-(6-methyl-2-quinolinyl)-1,3-indandione Solvent Green 3 128-80-3 AnasolGreen SG 1,4-di-p-toluidinoanthraquinone N/A 84-54-8 Anasol White SG2-methylanthraquinone

The compositions of the present invention also incorporate at least onebinder to provide the desired consistency. A binding agent from thegroup of the halogen-free thermoplastics can be used for the physicalstabilization of the mixture of the pyrotechnic smoke-producingcomposition. The binding agent can preferably be polyvinyl acetate,polyvinyl alcohol, polyvinyl butyral, polyvinyl ester, or polyvinylether. In the present invention, nitrocellulose is specificallydesirable in that it results in a decreased solid residue within theburned grain. Nitrocellulose is used in solution (6 to 12%nitrocellulose dissolved in acetone).

Binders of these types, in addition to providing desirable bindingcharacteristics, produce only a small energy output upon combustion.This is important in avoiding very high-energy outputs, hightemperatures, and flames, which render smoke producing compositionsdangerous and difficult to handle.

The composition of the present invention also includes one or moreoxidizer compounds. It is found that potassium chlorate (KClO₃) is anefficient oxidizer and produces good results when coupled with the fueland previously mentioned nitrogen-rich compounds.

The present invention includes a fuel. The fuel is preferably arelatively low energy fuel similar to the binder. It is also preferredthat the fuel produce gaseous reaction products capable of carrying thesmoke producing agent into the environment. Some suitable fuels includestarch, dextrose, and polyhydroxylic compounds such as lactose andsucrose.

Certain other materials may also be added to produce specific desirableresults. One suitable material is magnesium carbonate. Magnesiumcarbonate acts as a buffer, which prevents autocatalytic decompositionof the KClO₃. Magnesium carbonate also functions as a coolant when thesmoke-producing composition combusts. Alternatively, sodium bicarbonatecan be used. Another useful additive in the present invention isaluminum. In some cases, atomized aluminum can provide additionalthermal conductivity within the composition. This results in moreuniform heat transfer and ignition of the fuel.

In general, the ingredients of the composition may be within the rangesindicated in Table 2:

TABLE 2 Ingredient ranges of the improved pyrotechnic smoke- producingcomposition of the present invention Percent by Weight Materials (in drystate), % Nitrogen-Rich Compounds 5 to 15 Potassium Chlorate 20 to 35Sugar (Fuel) 15 to 25 Dye 27 to 40 Magnesium Carbonate 8 to 18Nitrocellulose 1 to 2

The following examples illustrate various embodiments of the invention,but it will be obvious that various changes and modifications may bemade therein without departing from the scope of the invention.

More specifically, excellent results are obtained with the formulationset forth in the following examples:

Example 1

Percent by Weight Materials (in dry state), % Guanidine Nitrate 3.8Guanidine Carbonate 3.8 Potassium Chlorate 24.9 Sugar 17.1 SolventOrange 7 32.9 Magnesium Carbonate 15.8 Nitrocellulose 1.7

Example 2

Percent by Weight Materials (in dry state), % Guanidine Nitrate 3.8Guanidine Carbonate 3.8 Potassium Chlorate 27.7 Sugar 18.7 Solvent Red 931.0 Magnesium Carbonate 13.3 Nitrocellulose 1.7

Example 3

Percent by Weight Materials (in dry state), % Dicyandiamide 9.0Potassium Chlorate 23.5 Sugar 16.0 Solvent Orange 86 32.9 MagnesiumCarbonate 16.8 Nitrocellulose 1.8

Example 4

Percent by Weight Materials (in dry state), % Dicyandiamide 9.0Potassium Chlorate 24.8 Sugar 17.0 Solvent Red 9 32.0 MagnesiumCarbonate 15.4 Nitrocellulose 1.8

Example 5

Percent by Weight Materials (in dry state), % Azodicarbonamide 10.0Potassium Chlorate 25.0 Sugar 17.0 Solvent Red 9 32.5 MagnesiumCarbonate 13.5 Nitrocellulose 2.0

Referring now to FIG. 1, the pyrotechnic smoke-producing compositionswere produced as follows: The process starts (12) by individuallyweighing (14) a quantity of nitrogen-rich compound(s) 16, a quantity ofoxidizer 18, a quantity of fuel 20, a quantity of dye 22, a quantity ofmagnesium carbonate 24, and a quantity of nitrocellulose 26. The weigheddry ingredients are then added to a mixing bowl (28) and undergo a firstmixing step (30). In the preferred embodiment, the mixer utilized as aHobart planetary gear-style mixer. Then, a quantity of acetone solvent32 (0.2-0.3 L/kg of the dry mix resulting from step 30) is measured (34)and subsequently added to the mixing bowl (36). The resulting mixtureundergoes a second mixing step (38). Initially, the mix is a veryviscous wet slurry of the components. As mixing proceeds, the acetonebegins to evaporate, and the composition assumes the consistency of wetdough. Mixing continues, and as more acetone evaporates, the doughycomposition breaks into increasingly smaller chunks. Mixing is furthercontinued until all visible acetone has evaporated and relatively dry,well-mixed spherical chunks of agglomerated mix have been produced. Theentire mixing process can be accomplished in approximately 25 minutesfor each kilogram of finished mixture when a 5-quart mixing bowl isused.

The composition's ingredients can also be blended together as drypowders using standard pyrotechnic techniques. However, the wet mixingtechnique using acetone is preferable because it is safer and produces amore homogeneous mixture.

The smaller spherical chunks are poured (40) from the mixing bowl intodrying trays. The mix is spread on the drying trays so the mix is flatat a uniform level in the trays. The trays are placed in an oven (42)maintained at 60±5° C. (140±10° F.), for 24 to 36 hours to evaporate anyresidual acetone. After drying, the material is ground (44) to achievesmall grains of pyrotechnic mixture, which can be further loaded orpreferably pelletized (46).

It has been found useful to pelletize the pyrotechnic composition ofthis invention, rather than to use the composition in powder form, toachieve predictable combustion performance of the composition.Pelletizing can be achieved by harshly mixing the powdered ingredientsand then using a pill press to produce pellets. Alternatively, thepowdered mixture can be granulated and then formed into noodles byextruding the mixture through a screen. Pelletizing has been foundadvantageous because the mixed powder has some undesirablecharacteristics. First, the powder tends to separate, with the oxidizerat the bottom and the fuel at the top. As a result, when the powderburns, it burns with different characteristics depending upon the degreeto which the powder mixture is homogeneous. Second, the powder may beloosely packed or tightly packed, which also affects its combustioncharacteristics. These variations in homogeneity and packing can lead toinconsistent combustion results when using the composition in powderform. When using the composition in pellet form, the combustion resultsare more consistent.

After drying, the pellets are hydraulically loaded (48) into grenadebodies 50 or pelletized to adjust the combustion characteristics of thecomposition so the devices have the required burning time. The loadapplied to the surface of the mix in the grenade body is about 5000 to7000 pounds per square inch (psi). A MIL SPEC No. 508 first fire startermixture or a flameless first fire starter mixture 52 is applied to thegrenades, and tops 54 are sealed onto the bodies (56). A No. 565 squibigniter 58 can be used to ignite the grenade. The loaded and sealedgrenades are the end result (60) of the process.

The colored smokes produced by the pyrotechnic compositions of thepresent invention were compared to smoke produced by conventionalformulations based on 1,4-benzendicarboxylic acid or aliphaticdicarboxylic acids. Each smoke color produced by the pyrotechniccompositions of the present invention was also compared to thecorresponding color standard FED-STD-595C color chip. This wasaccomplished by making the various pyrotechnic mixtures and forming theminto grenades in the manner previously described. The grenades were thenburned adjacent to one another to enable side-by-side visual comparison.The subjective evaluation of the color quality the smoke producedprovided a reliable indication of the improved effectiveness andefficiency of the pyrotechnic composition of the present invention.

Another indication of the greater efficiency of smoke munitions thatinclude the pyrotechnic compositions of the present invention was thelength of flaming time recorded during the burn. It was found thatflaming of the compositions of the present invention was reduced incomparison to the more frequent flaming of the standard mixtures basedon 1,4-benzendicarboxylic acid or aliphatic dicarboxylic acids. Theimproved effectiveness and efficiency of the composition of the presentinvention was shown throughout the comparison.

Various smoke-producing pyrotechnic compositions of the presentinvention, previously detailed above as Examples 1 to 5, were placed instandard military-style metal cans used for signal colored smokegrenade. The compositions were compacted as pressed pellets as a firstexperimental design, and as solid charges in a second experimentaldesign (see the second column of Table 3 below). In both experimentaldesigns, the weight of pyrotechnic filling was about 210 to 235 grams(7.5 to 8.2 oz.). The pressed or pelletized grains were ignited, andtheir burning characteristics, including ignition time and flame,burning time, burning temperature, can temperature and pressure wererecorded. The results of these tests are summarized in Table 3.

TABLE 3 Test results. Burning Can Ignition Burning TemperatureTemperature Flame, Time Time Range*** Range*** Experimental RangeRange*** (° C.) (° C.) Composition Design Type (sec) (sec) (° F.) (° F.)Remarks Example1 Pressed Pellets 2-5* 40-60 120-150 100-150 ** No topflame 250-300 200-300 Solid Charge 2-5*  90-110 120-150 100-150 ** Notop flame 250-300 200-300 Example2 Pressed Pellets 2-5* 50-70 100-140150-190 ** No top flame 200-275 300-375 Solid Charge 2-5* 100-120100-140 150-190 ** No top flame 200-275 300-375 Example3 Pressed Pellets2-5* 50-70 100-150 120-175 ** No top flame 200-300 250-350 Solid Charge2-5* 100-120 100-150 120-175 ** No top flame 200-300 250-350 Example4Pressed Pellets 2-5* 50-70 120-175 150-200 ** No top flame 250-350300-400 Solid Charge 2-5* 100-120 120-175 150-200 ** No top flame250-350 300-400 Example5 Pressed Pellets 2-5* 60-80 100-150 150-200 **No top flame 200-300 300-400 Solid Charge 2-5* 110-150 100-150 150-200** No top flame 200-300 300-400 *Includes 1.5 seconds to account forfuse delay. **qualitative evaluation determined visually, whichindicated good smoke yield, no burnt color, and good combustion pressurerange. ***temperatures were registered using a dual input thermometerdata logger model EXTECH EasyView 15 compatible with 7 types ofthermocouples.

The use of a flame retardant and a coolant within the coloredpyrotechnic smoke-producing composition of the current invention iscounterintuitive for two reasons. First, the goal of a coloredpyrotechnic smoke-producing composition is to burn with sufficientintensity to vaporize the dye component of the composition, so the useof ingredients that impede burning is contraindicated. Second, guanidinesalts, such as guanidine nitrate, are conventionally employed in the anof ignition as an exothermic reactant in a smoke grenade (U.S. Pat. No.4,238,254), or as an additional fuel for a flare igniter (U.S. Pat. No.6,170,399). This makes their usage in the current invention for theirflame retardant properties nonobvious.

While current embodiments of a colored pyrotechnic smoke-producingcomposition and methods of preparation have been described in detail, itshould be apparent that modifications and variations thereto arepossible, all of which fall within the true spirit and scope of theinvention.

With respect to the above description then, it is to be realized thatthe optimum dimensional relationships for the parts of the invention, toinclude variations in size, materials, shape, form, function and mannerof operation, assembly and use, are deemed readily apparent and obviousto one skilled in the art, and all equivalent relationships to thoseillustrated in the drawings and described in the specification areintended to be encompassed by the present invention.

Therefore, the foregoing is considered as illustrative only of theprinciples of the invention. Further, since numerous modifications andchanges will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction and operationshown and described, and accordingly, all suitable modifications andequivalents may be resorted to, falling within the scope of theinvention.

I claim:
 1. A pyrotechnic flameless ignition composition comprising: anoxidizer; a fuel; a flame retardant; a dye; a coolant; and a binder. 2.The composition of claim 1 wherein the oxidizer is potassium chlorate.3. The composition of claim 1 wherein the fuel is at least one of thegroup consisting of starch, dextrose, lactose, and sucrose.
 4. Thecomposition of claim 1 wherein the coolant is selected from the groupconsisting of sodium bicarbonate and magnesium carbonate.
 5. Thecomposition of claim 1 wherein the binder is selected from the groupconsisting of nitrocellulose, polyvinyl acetate, polyvinyl alcohol,polyvinyl butyral, polyvinyl ester, and polyvinyl ether.
 6. Thecomposition of claim 1 wherein the dye is selected from the groupconsisting of amethoxybenzenazo-β-naphthol, 1-methylaminoanthraquinone,1-((2,4-Dimethylphenyl)azo)-2-naphthalenol, 1,4-dihydroxyanthraquinone,1-methylamino-4-ethanolaminoanthraquinone,1,4-diamino-2,3-dihydroanthraquinone, a mixture of2-(2-quinolinyl)-1,3-indandione and2-(6-methyl-2-quinolinyl)-1,3-indandione,1,4-di-p-toluidinoanthraquinone, and 2-methylanthraquinone.
 7. Thecomposition of claim 1 wherein the flame retardant is at least one ofthe group consisting of guanidine nitrate, guanidine carbonate,dicyandiamide, azodicarbonamide, melamine, and oxamide.
 8. Thecomposition of claim 1 wherein the composition is in pelletized form. 9.The composition of claim 1 wherein the composition comprises on a massbasis oxidizer 20-35%, fuel 15-25%, flame retardant 5-15%, dye 27-40%,coolant 8-18%, and binder 1-2%.
 10. A colored smoke-producingpyrotechnic device comprising a body filled with the composition ofclaim 1 and a first fire starter composition, and an attached squibigniter.
 11. The device of claim 10 wherein the composition of claim 1filling the body is in the form of pressed pellets.
 12. The device ofclaim 10 wherein the composition of claim 1 filling the body is in theform of a solid charge.
 13. The device of claim 10 wherein the body is agrenade.
 14. A process for producing a pyrotechnic flameless ignitioncomposition comprising the steps of: obtaining a quantity of oxidizer;obtaining a quantity of fuel; obtaining a quantity of flame retardant;obtain a quantity of dye; obtaining a quantity of coolant; obtaining aquantity of binder; and adding the quantities of oxidizer, fuel, flameretardant, dye, coolant, and binder together to form a dry mix.
 15. Theprocess of claim 14 further comprising the steps of: obtaining aquantity of liquid; adding the quantity of liquid to the dry mix to forma first mixture; and mixing the first mixture until all visible liquidhas evaporated to form a second mixture.
 16. The process of claim 15further comprising the steps of: obtaining a drying tray; pouring thesecond mixture into the drying tray; and drying the second mixture untilany residual liquid has evaporated.
 17. The process of claim 16 furthercomprising the step of grinding the dried second mixture.
 18. Theprocess of claim 17 further comprising the steps of: pelletizing theground second mixture; obtaining a body; loading the second mixturepellets into the body; loading a first fire starter composition into thebody; sealing the body; and attaching an igniter to the grenade.
 19. Theprocess of claim 17 further comprising the steps of: obtaining a body;loading the ground second mixture into the body as a solid charge;loading a first fire starter composition into the body; sealing thebody; and attaching an igniter to the grenade.
 20. The process of claim15 wherein the quantity of liquid is at least 0.2 L per kilogram of drymix and is less than 0.3 L per kilogram of dry mix.
 21. The process ofclaim 20 wherein the liquid is acetone.
 22. The process of claim 14wherein the dry mix comprises on a mass basis oxidizer 20-35%, fuel15-25%, flame retardant 5-15%, dye 27-40%, coolant 8-18%, and binder1-2%.